Molded plastic parts are utilized in many manufacturing processes. In machinery manufacturing processes, such as the manufacture of automotive vehicles, the plastic parts are attached to other components of the vehicle to create the final assembled product. The attachment of the molded plastic parts to other components typically requires the utilization of fasteners attached to the molded plastic part to permit a selective detachable connection to the component on which the plastic part is to be mounted.
Molding of the plastic part can be accomplished in one of several known processes, including injection molding and blow molding, which can provide finished plastic parts. It is known in the art of molding plastic components to place a fastener into the mold to permit the plastic material to flow around the fastener head and, thereby, incorporate the fastener directly into the molded plastic part. This process is commonly referred to as insert molding. Fasteners having conventional hex heads, square heads, or even carriage heads have been utilized in the insert molding process. By encapsulating the fastener head into the plastic component and leaving the threaded shank of the fastener exposed externally of the plastic part, the molded plastic part can be easily attached to any component having a suitable opening into which the threaded shank can pass for attachment thereto.
Conventional fasteners suffer from the problem of having high profiles on the head portion, thus requiring substantially thicker plastic components to encapsulate the head portion. Conventional fasteners also suffer from having low spin-out torque values, e.g. the amount of torque applied to the threaded shaft of the fastener that will cause the head portion to break away from the plastic encapsulation. Conventional fasteners typically have a relatively high pull-out force values, e.g. the amount of force required to pull the fastener out of the molded plastic component. Pull-out forces are resisted by the size and shape of the head portion of the fastener over which the plastic is encapsulating. Generally, the larger and flatter the head portion is on the underside of the head portion.
Spin-out forces are typically resisted by the shape of the head portion. For example, a carriage head having a round, semi-circular head would have a relatively low spin-out torque value. Square-headed fasteners, however, have a relatively high spin-out torque value because of the shape of the corners embedded into the plastic material forming the molded component. Hex-head fasteners would, therefore, have an intermediate spin-out torque value between a carriage head and a square head.
Another problem associated with the insert molding of fasteners into plastic components is the localized stress created in the plastic material by the shape of the head portion of the fastener. Square-headed fasteners, for example, have a significant amount of localized stress at the corners of the head portion where the plastic material has to flow around the sharp corner of the head portion. Thus, a carriage head fastener would generate much lower localized stresses in the plastic material, but have a highly undesirable spin-out torque value for most plastic part applications in the automotive industry.
Prior art fasteners have been provided with a variety of head shapes into which a wide variation of recesses are formed for engagement of tools for manipulating the fasteners. Such fastener configurations are found in U.S. Pat. No. 1,910,182, ranted to Peter Robertson on May 23, 1933, in which the recess in the head portion is adapted to be engaged by either a flat-head screwdriver or a square socket driver. In U.S. Pat. No. 2,556,155, issued to Domnic Stellin on Jun. 5, 1951, a variety of recess shapes are disclosed to increase the utilization of the fastener with differently shaped sockets and/or screwdrivers. Similarly, U.S. Pat. No. 5,358,368, issued to Gary Conlin, et al on Oct. 25, 1994, teaches a fastener head that can be engaged with either a flat-head or Philips-type screwdrivers or by a square socket driver. Substantially the same head configuration is taught in U.S. Pat. No. 5,674,037, issued to Cheug-chuan Lu on Oct. 7, 1997, except that the linear slot for the engagement of a flat-head screwdriver is oriented diagonally with respect to the Philips recess and the socket recess.
Other fastener configurations are taught in U.S. Pat. No. 5,713,705, issued to Carl Grunbichler on Feb. 3, 1998, in which the high profile head portion is formed with a narrow portion creating a torque limiting effect in which the upper half of the head portion can separate from the lower half. A fastener with compound recesses in the head portion is disclosed in U.S. Pat. No. 6,302,632, issued to Chao-Wei Lin on Oct. 16, 2001, could provide increased spin-out torque resistance with the convoluted head recesses, but would suffer substantially from localized stresses in the plastic material if utilized in an insert molding process due to the sharp angles formed in the head portion. A particularly formed sidewalk bolt is disclosed in U.S. Pat. No. 6,682,283, issued to Gregory Mann, et al on Jan. 27, 2004, although the rounded head would provide little resistance to spin-out torque in an insert molding utilization. A compound, multiple part fastener used for mounting hybrid composite access panels is depicted in U.S. Pat. No. 5,569,008, issued on Oct. 25, 1996, to John Chapkovich.
Accordingly, it would be desirable to provide an improved fastener configuration that would be particularly effective in utilization with insert molding processes, while providing high spin-out torque and pull-out force values with minimal localized stress in the plastic material encapsulating the portion of the fastener.